Field of the Invention
The present invention relates to a four-cycle OHV engine preferable for an outboard motor and a similar device to which an internal combustion is mounted as a power source.
Description of the Related Art
As a relief structure of lubricating oil in a so-called vertical engine where a crankshaft is vertically placed, for example, a relief structure described in Patent Document 1 has been known. This relief structure couples an oil pump at a lower end of a camshaft. A pump chamber disposed at a lower side of a cam journal houses this oil pump. A wall that couples a crank journal, the cam journal, and an oil filter is formed integrally with a lower crankcase so as to partition an inside of this lower crankcase. Oil passing holes that communicate with the crank journal, the pump chamber, and the oil filter are formed on the inner wall. At one side of the wall between the crank journal and the cam journal, an outlet side of a relief hole communicating with the oil passing hole is open.
To process the relief structure according to Patent Document 1, concurrently with a process of linearly coupling the crankshaft of the crankcase, the camshaft, and the oil filter, a process of coupling an oil relief hole, the camshaft, and the oil filter is given.
Patent Document 1: Japanese Registered Utility Model No. 25009%5
The vertical engine with the conventional lubricating oil relief structure includes the oil filter on an extended line coupling the crankshaft and the camshaft; therefore, the oil filter projects outside and there is no choice but to increase an engine size. To mount a relief valve for lubricating oil, processing is required to an inside of the lower crankcase in a crankshaft direction, causing a problem such as an increase in the number of man-hours for the process.